The invention relates to a Coriolis-type mass flow meter and, in particular, to such a meter comprising at least two straight parallel vibrating tubes.
These meters can be used, in particular, for the monitoring of multi-phase flows in flow lines. Coriolis-type mass flow meters comprising one straight vibrating tube are already known. These meters are based upon the following principle: The flow to be measured flows through a straight tube which is part of a flow line. The ends of the tube are clamped. The tube itself is adapted to be excited at 50 percent of its length and vibrates at or near its resonance frequency. A mass flow through the tube causes distortion of this forced vibration and a phase difference to occur between the upstream and downstream part of the tube, which is proportional to mass flow. The theoretical relations between mass flow rate and phase difference are known to those skilled in the art and will not be explained in detail. The length of the meter is a critical parameter: the meter sensitivity increases proportionally to the total tube length and in multi-phase flow a minimum length-to-inner diameter ratio is required.
However, for practical applications the length of the meter should be limited and therefore the diameter of the vibrating tube must be reduced with respect to the flow line diameter. For one straight vibrating tube, this results in too high a pressure loss in the meter, which may cause serious measuring problems.
It is therefore an object of the invention to provide a Coriolis-type mass flow meter of restricted length, which is suitable to be used for monitoring multi-phase flow and can be handled easily.